The present invention relates to the field of digital imaging and, more precisely, to representing one or more digital images in a plurality of image processing states through the use of residual images.
In forming digital images, an input digital image (in a predetermined image processing state) can be processed through a series of digital image processing enhancement steps. At the output of each digital image processing enhancement step, a digital image in another image processing state is produced. The image processing state inherent in any digital image is the result of the image source and the image processing that has been applied to the image, and is an indicator of the image information attributes retained in the image. For example, a digital image from a digital camera in a first, unsharpened, image processing state, can be processed by a digital image processing system that sharpens the digital image to produce a digital image in a second, sharpened, image processing state. If desired, this digital image can be processed by subsequent digital image processing enhancement steps where, for example, it can be color corrected, defect corrected, resampled, etc., to form a series of digital images in different image processing states. This arrangement is well known in the art. For example, see Delp (U.S. Pat. No. 5,420,967).
Generally, digital image processing systems produce a single digital image in some final image processing state. The final digital image can be stored in a digital storage device and/or displayed on an output device. A problem with this digital image processing scheme is that it lacks flexibility; it is not possible to go back at a later time and change any of the intermediate processing operations. For example, the digital image processing enhancement steps needed to produce an optimal digital image for one output device may produce a digital image that is sub-optimal for a different output device. For example, it may be desirable to apply a greater amount of sharpening for one output device and a lesser amount of sharpening for a different output device.
An alternative to the above image processing scheme is to store multiple digital imagesxe2x80x94each representing a different image processing state. Though this approach permits the digital image processing enhancement steps to be tailored for different uses, it has the disadvantage that a relatively large amount of digital memory can be required to store the full set of digital images.
Various other methods have been developed to provide some means of adapting a digital image from one intended use to another. For example, certain image processing operations may make use of non-image information, conveying image characteristics, in order to properly adapt subsequent processing parameters when modifying the digital image for another use. Non-image information, or metadata, refers to data that is carried along with each digital image and provides information about the capture conditions, capture devices, expected noise statistics, prior image processing operations, etc. An example of this type of image processing operation is image-dependent sharpening, where a measure of the imaging chain Modulation Transfer Function (MTF) could be used to adaptively change the sharpening applied to the digital image. During the processing of image information in a multi-stage imaging system, however, the non-image data is usually affected by every operation or transformation applied to the digital image. If this impact on the non-image data is not taken into account, then subsequent operations that make use of these data will not operate as intended and system performance (i.e. image quality) may suffer.
Another approach to providing flexible image processing that is well-known in the art involves the creation of a list of image processing commands, i.e., an image processing script, that is associated with the unchanged original digital image. In this case, the image processing script is applied to a copy of the original digital image to produce one desired output. When an alternative output is desired, the script can be modified and a copy of the original digital image can be processed through the revised script to create the alternative output. One drawback of this approach is that, as a digital image is conveyed from one imaging system to another, the interpretation of the commands in the associated image processing script may vary. This may result in unacceptable changes in the appearance of the digital image when it is processed through the script and displayed. Another disadvantage to this approach is that the digital image must always be processed before it is ready for use. This may result in unacceptable decreases in system throughput.
In general, when an image is rendered for a particular output, device characteristics pertinent to that output are used in that rendering. For example, the color gamut of the device and the MTF and resolution of the device, may be used to determine the color encoding and final sharpening applied to the image, respectively. As a result, a device-specific output prepared from an original image is typically preferred over a second-generation output prepared from a previously determined output image.
It is an object of the present invention to overcome the limitations of the prior art by providing a flexible arrangement for representing digital images in a plurality of image processing states. It has been recognized that the drawbacks of the prior arrangements can be mitigated, by providing a way to revise or redirect the intermediate image processing operations used to produce the final digital image.
This object is achieved by a method for representing a digital image in a plurality of image processing states using at least one reference digital image and at least one residual image comprising the steps of:
a) manipulating an input digital image using at least one digital image processing enhancement step to form at least one additional digital image in a different image processing state;
b) designating at least one of the digital images to be a reference digital image in a reference image processing state; and
c) determining at least one residual image representing differences between one of the reference digital images and one of the additional digital images, whereby the residual image(s) and the reference digital image(s) can be used to form digital image(s) in different image processing states.
It is an advantage of the present invention that, by using at least one residual image and at least one of the reference digital images, digital images can be formed in different image processing states. These image processing states can be reconstructions of original image processing states or can be new image processing states.
It also has the advantage that information about multiple, different image processing states can be retained without needing to store a full image for each different image processing state in digital memory.
It has the further advantage that a special rendering engine is not required to process a digital image from one image processing state to another.
It has the additional advantage that the use of the residual image(s) is optional. As a result, the benefits of the residual image(s) can be gained by applications that are able to make use of the information, without introducing an image-quality or computational penalty for applications that do not require the optional information or that are not able to make use of it.